It is known to make absorbent pads with flow-spreading depressions or projections. Sanitary napkins, baby diapers and the like have been made with cellulose fluff or crepe wadding material between a cover sheet and a plastic back sheet, and with the absorbent medium embossed with depressions extending parallel to the longitudinal axis of the pad, transverse thereto, or in various patterns such diamond, herringbone, sinusoidal, etc. Examples of methods and apparatus for making such products are shown in U.S. Pat. Nos. 2,627,858, 2,978,006, 3,221,738, 3,315,676, 3,670,345, 3,729,005, 4,033,709, 4,275,811, 4,382,507 and 4,392,862.
These patents teach the embossing of a continuous mat of absorbent material by depressing a portion of the mat under an embossing roller having the required pattern to create the channels of the intended configuration. This not only created flow channels, but also helped to integrate the mat and prevent balling of the cellulose into one end of the bag created by the cover and back sheets. A method and machine for creating such embossed channels is shown in U.S. Pat. No. 4,331,501.
Various patterns and designs of the flow channels themselves are shown in U.S. Pat. Nos. 3,881,490, 4,059,114, 4,079,739, 4,211,227 4,381,783, and Des. 247,368.
It is also known to moisten the cellulose under the embossing roller so as to increase the density of the cellulose and improve the wicking or flow spreading characteristics of the channels. This is disclosed in U.S. Pat. Nos. 2,952,260 and 3,060,936.
It is further known to apply these principles to hospital bed pads, rather than to diapers, as shown by U.S. Pat. Nos. 4,327,732 and Re. 30,972.
In all of these products, the absorbent mat was continuous prior to embossing and so was continuous after embossing, that is, the mat was not separated into separate islands but extended continuously between the cover and back sheets and across the channel regions.
A variation on the constructions discussed above involved the application of lines of glue or other adhesive to the plastic backing sheet to hold the absorbent mat in place. Usually such lines were parallel to the longitudinal extent of the pad, but a diamond pattern is shown in U.S. Pat. No. 3,881,487. In this patent, the channels are filled with adhesive and thus the flow of liquid through the channels is impeded.
It is further known, as in U.S. Pat. No. 4,321,997, to provide diamond-shaped islands of absorbency isolated by a lattice-like network of plastic net which fills the channels between the islands and so does not provide flow-enhancing grooves.
Islands of absorbent material are also shown in U.S. Pat. No. 4,338,377, held between two sheets of web material.
U.S. Pat. No. 4,560,372 discloses a pad wherein a lattice-like network of absorbent fibers and super-absorbent material is expanded to form areas of absorbency in the channels with the islands between such areas being void.
Finally, U.S. Pat. No. 4,360,021 discloses an embossed plastic sheet which provides tiny depressions having small quantities of superabsorbent material in the depressions. A cover of non-woven material is disposed over the depressions and the liquid is discharged directly onto the cover and into the depressions. As one depression is filled and the liquid absorbed by the filling material, excess liquid spills over into the next adjacent depression, and continues until the liquid is fully absorbed in the nearest depressions. Such a structure has no channels for flow of the liquid.